Point Defense

Can anyone shed some light on how point defense works in terms of targeting? To be more specific, I notice only one system from one ship engages a given missile. If this pd misses, the missile will strike the second ship even if it has unfired point defense weapons ready. If this is true it would significantly change ship builds since adding in one or two pd weapons as a backup may actually void the fire of a ship built for pd if the backup should fire first thus giving a lower chance to stop the missile. Thanks in advance!